Table of Contents
pnmtopng - convert a portable anymap into a Portable Network Graphics
file
pnmtopng [-verbose] [-downscale] [-interlace] [-alpha file]
[-transparent [=]color] [-background color] [-gamma value]
[-hist] [-chroma wx wy rx ry gx gy bx by] [-phys x y unit]
[-text file] [-ztxt file] [-time [yy]yy-mm-dd hh:mm:ss]
[-filter type] [-compression level] [-force] [pnmfile]
Reads a
portable pixmap as input. Produces a Portable Network Graphics file as output.
Color values in PNG files are either eight or sixteen bits wide, so pnmtopng
will automatically scale colors to have a maxval of 255 or 65535. Grayscale
files will be produced with bit depths 1, 2, 4, 8 or 16. An extra pnmdepth
step is not necessary.
- -verbose
- Display the format of the output file.
- -downscale
- Enables scaling of maxvalues of more then 65535 to 16 bit. Since
this means loss of image data, the step is not performed by default.
- -interlace
- Creates an interlaced PNG file (Adam7).
- -alpha file
- The alpha channel of
pixel (or image) specifies the transparency of a pixel. To create this fourth
pixel value a separate .pbm- or .pgm-file is needed. In this file black (0)
stands for fully transparant and white (1)
will become opaque. The sizes
of both pbm/pgm/ppm-files must be the same. If the information contained
in the alpha mask can also be represented as a transparency index, it will
be used, since this should result in a smaller image file.
- -transparent color
- ppmtogif marks the specified color as transparent in the PNG image.
You
specify the color as in ppmmake(1)
.E.g. red or rgb:ff/00/0d. If the color you
specify is not present in the image, pnmtopnm selects instead the color
in the image that is closest to the one you specify. Closeness is measured
as a cartesian distance between colors in RGB space. If multiple colors
are equidistant, pnmtopnm chooses one of them arbitrarily.
However, if
you prefix your color specification with "=", e.g.
-transparent =red
Only
the exact color you specify will be transparent. If that color does not
appear in the image, there will be no transparency. pnmtopng issues an
information message when this is the case.
- -background color
- To create
a background color chunck in the png-file, which can be used for subsequent
alpha-channel or transparent-color conversions. See -transparent for format
of color.
- -gamma value
- Creates an gAMA chunk. By providing the gamma-value
of the pnm-file the software that lateron will display the png-file will
be able to do the necessary gamma-corrections. A good rule-of-thumb is that
when the file is created by a software program (like a CAD-program or a
ray-tracer) the value is probably 1.0. When the pnm-file looks good on a non-gamma
corrected PC display (which has itself a gamma-value of 2.2 - 2.8), a value
of 0.45 should be given.
- -hist
- Use this parameter to create a chunk that specifies
the frequency (or histogram) of the colors in the image.
- -chroma white point
X and Y, red X and Y, green X and Y, and blue X and Y
- To specify the white
point and rgb values following the CIE-1931 spec.
- -phys x y unit
- When your
image should not be displayed with square but with rectangular pixels this
option should be used to create a pHYS chunk. When the unit-value is 0 the
x and y only gives the ratio of pixel width and height. When it is 1 the
x and y specify the number of pixels per meter.
- -text file
- Allows to include
comments in the text-chunk of the png-file. The format of the text-file is
as follows: when the first column does not contain a blank or a tab, the
first word is considered to be the keyword. For keywords to contain spaces,
enclose them in double-quotes.
When the first character on a line is a blank or tab, the rest of the line
is a new line of the current comment. Note that the initial spaces are not
considered to be part of the comment line.
Here is an example:
-------------------------------------------
Title PNG-file
Author your name
Description how to include a text-chunk into a PNG file
"Creation date" 3-feb-1987
Software pnmtopng
-------------------------------------------
- -ztxt file
- The same as -text, but now the text will be compressed.
- -time yy-mm-dd
hh:mm:ss or -time yyyy-mm-dd hh:mm:ss
- This option allows you to specify the
(modification)time. The year parameter can be given as a two- or a four-digit
value.
- -filter type
- When the types of filters must be restricted you can
specify here which filter you want to use. Allowed values are: 0 (none),
1 (sub), 2 (up), 3 (avg) and 4 (paeth).
- -compression level
- To explicitly
set the compression level of zlib use this parameter. Select a level between
0 for no compression (max speed) and 9 for maximum compression.
- -force
- When
set, -force limits the optimizations of pnmtopng. A png-file similar to the
pnm-input is as much as possible enforced. For example no paletted files
will be created and alpha-channel images will not be converted to images
with a transparency chunck.
All flags can be abbreviated to their shortest
unique prefix.
pngtopnm(1)
, gif2png(1)
, pnmgamma(1)
, pnm(5)
Instead
of xxxtopnm|pnmtopng, a specific converter should be used, if available.
E.g. gif2png (GIF conversion), etc.
There could be an option to read the
comment text from pnm comments instead of a separate file.
The program could
be much faster, with a bit of code optimizing.
Copyright (C) 1995-1997
by Alexander Lehmann
and Willem van Schaik.
Table of Contents